When you disable/remove any service, the classes are not loaded into memory and services do not start. To slim down the services from standalone-*.xml file, comment/remove the extension of the service and its subsystem.

No, if you would like to reduce the JBoss process size, you can consider to reduce the max heap size or perm/metaspace size. However, that needs monitoring of memory usage and accordingly you can reduce the size. Reducing the heap or perm/metaspace value to very low could cause outofmemory:heap/perm/metaspace error though.